Field of the Invention
The present invention relates to an electromagnet control apparatus that controls current to an electromagnet mounted in a construction machine.
Description of the Related Art
A conventional lifting magnet driving circuit includes a direct-current conversion unit that converts an alternating power supply voltage into a direct-current power supply voltage, an H-bridge circuit that controls the direction of magnetizing current to a lifting magnet, an energy absorption unit that has a transistor and a resistance element connected to each other in series and a capacitor connected in parallel with the transistor and the resistance element, the energy absorption unit absorbing energy accumulated in the lifting magnet when the direction of magnetizing current is changed, and a control unit that controls continuity in the transistor of the energy absorption unit based on the direction and amplitude of current passing through a positive-side power supply line between the H-bridge circuit and the energy absorption unit and a potential difference between the positive-side power supply line and a negative-side power supply line (for example, see Japanese Patent Laid-Open No. 2007-119160).
If the arm or the like of a construction machine is operated during the control of the lifting magnet (hereinafter, will be called a composite operation), unfortunately, the conventional lifting magnet driving circuit reduces the flow rate of oil supplied to the power generator of a construction machine and reduces a voltage applied across the lifting magnet. This may cause the control unit to change a control state from magnetization to counter-magnetization (demagnetization) regardless of the intention of an operator so as to release pieces of iron attracted to the lifting magnet.
The present invention has been devised to solve the problem and provides an electromagnet control apparatus that can suppress a change of a control state from magnetization to counter-magnetization by a control unit regardless of the intention of an operator during a composite operation of a construction machine.